There is implementation divergence in the handling of the following example:

  template <typename T>
  concept C = true;

  template <typename T>
  void f() requires C<T *> {
   //
  }

  void g() {
   f<int &>();
  }

Is the constraint not satisfied because an intermediate invalid type "pointer to reference to T" is formed? Or is the constraint satisfied because T is never actually used?